Unconventional reservoirs often have a low-permeability rock matrix that impedes fluid flow, making it difficult to extract hydrocarbons (or other fluids of interest) at commercially-feasible rates and volumes. Fortunately, the effective permeability of the formation can be increased by hydraulic fracturing. When the rock matrix is exposed to a high-pressure high-volume flow of a relatively incompressible fluid, the low permeability causes sharp gradients in the formation's stress field, forcing integrity failures at the relatively weakest points of the rock matrix. Such failures often occur as sudden “cracking” or fracturing of the matrix that momentarily reduces the stress gradient until it can be rebuilt by the intruding fluid flow. As the high-pressure flow continues, the fractures may propagate, for example, as an intermittent series of small cracks. The injected fluid also deforms and shifts blocks of matrix material, further complicating the fracture propagation analysis.
Accordingly, accurate modeling of the hydraulic fracturing operation requires that fluid flow phenomena be taken into account. However, the computation resources available for modeling are typically limited and the challenge is to maximize the accuracy and efficiency of the modeling process within these constraints, and to ensure that the accuracy is sufficient to guide oilfield operators.
Oilfield operators generally desire to provide a relatively even distribution of fractures throughout the reservoir while avoiding overlap in the fractures connecting to different wells or different production zones in a single well. (Such overlaps prevent operators from applying a pressure differential across the region between the overlapping fracture families, dramatically reducing the rate and efficiency at which fluid can be drained from that region. Conversely, an uneven distribution of fractures leaves regions of low permeability that similarly cannot be drained effectively.) Thus, operators seek to induce fracturing with carefully controlled fracture reach (“extent”). Inaccuracies in predicting and controlling fracture extent significantly impair the efficiency and rate at which fluids can be recovered from the formation.
It should be understood, however, that the specific embodiments given in the drawings and detailed description do not limit the disclosure. On the contrary, they provide the foundation for one of ordinary skill to discern the alternative forms, equivalents, and modifications that are encompassed together with one or more of the given embodiments in the scope of the appended claims.